Autonomic signatures of late preterm, early term, and full term neonates during early postnatal life

Abstract

Background: Late preterm and early term births account for ~25% of live births. Infants born prior to term are at significantly higher risk for subsequent morbidity and mortality.

Aims: Determine autonomic regulation differences in infants (35-40 weeks gestation) during sleep at birth and one-month after delivery.

Study design: Consecutive enrollment until at least 20 infants per group: 75 late preterm (35-36 weeks gestation), 110 early term (37-38 weeks), and 130 full term (39-40 weeks). Assess autonomic parameters 12-84 h after delivery and again at one month of life.

Subjects: 329 newborns met inclusion criteria.

Exclusions: maternal age < 18 years, major maternal medical problems, psychiatric medications, drug use, Apgar <8 at 5 min, medical complications requiring other than standard care, non-English or non-Spanish speaking.

Outcome measures: Heart rate and two measures of heart rate variability in active and quiet sleep at birth and at one month of life.

Results: Late preterm and early term newborns demonstrate immature patterns of autonomic regulation at birth. Heart rate decreased with gestational age in both sleep states whereas the standard deviation of R-R intervals and beat-to-beat variability in heart rate both increased with gestational age in both sleep states. One month after delivery, i.e. at term-equivalent age, late preterm infants continued to have higher heart rates than infants born full term; and their heart rate was also significantly higher when compared to that of full term newborns at birth, i.e. their autonomic signature did not "normalize" over the first four weeks of life. Early term infants, however, did not differ from full term infants when they reached a postmenstrual age of 44 weeks.

Conclusion: The specific patterns of immature autonomic regulation in late preterm and early term infants during early postnatal life may underlie their increased morbidity and mortality in infancy and later in development. Future studies should address how early autonomic measures might relate to adverse outcomes. Results suggest the need for autonomic nomograms at birth and at one month after delivery that are stratified by both gestational week and sleep state.

Keywords: Autonomic nervous system; Early term; Heart rate; Heart rate variability; Late preterm; Neonatal development.